The present invention relates to a light source provided with an ultraviolet visible excitation light generation unit for generating first visible light and ultraviolet light and a fluorescence generation unit having a phosphor screen that generates second visible light when ultraviolet visible light generated from the excitation light generation unit irradiates the phosphor screen as excitation light and a display using the light for a light source for a liquid crystal display (a backlight of a liquid crystal display panel).
To display a color image on a liquid crystal display, a light source (a backlight) for a liquid crystal display is essential. Recently, the miniaturization and the enhancement of the quality of the light source are demanded. To enhance the quality of a liquid crystal display as a display, the quantity of white light emitted from a light source is required to be further enhanced.
To enhance the quality of an image and the luminance, the optimization of the color temperature of white light and the enhancement of a luminance saturation characteristic, a luminance degradation characteristic and a decay characteristic are required. The luminance saturation and degradation characteristic greatly differs depending upon the type, the manufacturing process, the dopant and the composition of phosphor material.
To improve these, the selection of phosphor having a better characteristic and the improvement of the composition and the manufacturing process have been discussed. To improve these defects, proposal that phosphor is excited by blue light from a blue light emitting diode (hereinafter called blue-LED) made of gallium nitride for example and white light is acquired is made and the practical use is discussed.
This is disclosed in Japanese published unexamined patent application No. Hei 10-269822 for example. It is known that at this time, for phosphor material, (Y,Gd)3(Al,Ga)5O12:Ce phosphor the luminance degradation of which is small is used. This phosphor emits yellow-green light and white light can be acquired by mixing the yellow-green light and the blue light from the blue-LED.
However, there is a problem that the color temperature of the white light at this time is not enough and the quality of an image of a liquid crystal display is not enough. Therefore, there is a problem that for a white light source, a color reproduction area is small and particularly, the color purity of red is not satisfactory. Also, as it is important for a light source to maintain stable luminance for a long time, a luminance characteristic is also required to be improved.